Aquarium



FIG. 1 is a front elevational view of an aquarium showing my new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a left side view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken lines shown in the figures represent portions of the aquarium that form no part of the claimed design. 

The ornamental design for an aquarium, as shown and described. 